Method and apparatus for generating computer-generated hologram

ABSTRACT

Disclosed are a method and a system for processing a computer-generated hologram (CGH). The system for processing a CGH includes a CGH generation apparatus and a display apparatus. The CGH generation apparatus repeatedly performs a process of propagating object data from a first depth layer to a second depth layer, changing amplitude data of the object data to second predefined amplitude data, back-propagating the object data from the second depth layer to the first depth layer, and changing the amplitude data of the object data to first predefined amplitude data, and generates a CGH by using the object data.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims priority under 35 U.S.C. § 119to Korean Patent Application No. 10-2020-0104805, filed on Aug. 20,2020, and Korean Patent Application No. 10-2021-0041261, filed on Mar.30, 2021, in the Korean Intellectual Property Office, the disclosures ofwhich are incorporated by reference herein in their entirety.

BACKGROUND 1. Field

The disclosure relates to a method and a system for processing acomputer-generated hologram (CGH).

2. Description of Related Art

Holography is a 3D space representing technology to reproduce an objectin a 3D space by adjusting the amplitude and phase of light.Accordingly, a user may have an unrestricted view and may not experience3D visual fatigue. Therefore, devices that realize high-resolutionholographic images in real-time by using a complex spatial lightmodulator (SLM) capable of simultaneously controlling the amplitude andphase of light have been developed. A hologram may be displayed in a 3Dspace by using an interference pattern formed between an object wave anda reference wave. Recently, computer-generated holography that mayprovide a hologram on a flat panel display by processing an interferencepattern for reproducing a hologram has been utilized. In a method ofgenerating a digital hologram, for example, a computer-generatedholography method, a hologram is generated by approximating opticalsignals and computing an interference pattern generated by mathematicalcalculations based on the approximated optical signals. In the methodfor generating a digital hologram, since an object consists of a set ofvarious data such as 3D points, polygons, or depth data, a completedhologram is generated by calculating pieces of object data constitutingthe object.

SUMMARY

Provided are a method and a system for processing a computer-generatedhologram (CGH). The objectives of the disclosure are not limited to thetechnical objects described above, and other technical objects may beinferred from the following embodiments.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of embodiments of the disclosure.

In accordance with an aspect of the disclosure, a method for processinga computer-generated hologram (CGH) includes obtaining a first objectimage corresponding to a first depth layer and a second object imagecorresponding to a second depth layer; determining first predefinedamplitude data based on the first object image and second predefinedamplitude data based on the second object image; generating first objectdata including the first predefined amplitude data and randomized firstphase data; and performing a propagation process using the first objectdata as an input, the propagation process including propagating thefirst object data to the second depth layer to obtain second object dataincluding second amplitude data and second phase data; replacing thesecond amplitude data with the second predefined amplitude data toobtain changed second object data; back-propagating the changed secondobject data to the first depth layer to obtain changed first object dataincluding changed first amplitude data and changed first phase data; andreplacing the changed first amplitude data included in the changed firstobject data with the first predefined amplitude data to obtain finalfirst object data, wherein the method further includes generating a CGHbased on the final first object data; and displaying a first holographicimage including the first predefined amplitude data and a secondholographic image including the second predefined amplitude data basedon the CGH.

The method may further include performing the propagation process apredefined number of times using the final first object data of apreceding iteration of the propagation process as the input before thegenerating of the CGH.

The propagation process may further include determining a differencebetween the changed first amplitude data and the first predefinedamplitude data; and repeating the propagation process using the finalfirst object data of a preceding iteration of the propagation process asthe input based on the determined difference being greater than or equalto a predefined threshold value.

The propagation process may further include determining a differencebetween the changed second amplitude data and the second predefinedamplitude data; and repeating the propagation process using the finalfirst object data of a preceding iteration of the propagation process asthe input based on the determined difference being greater than or equalto a predefined threshold value.

The propagating of the first object data may include performing a fastFourier transform (FFT) on the first object data, and theback-propagating of the changed second object data may includeperforming an inverse FFT on the changed second object data.

The obtaining of the first object image and the second object image mayinclude obtaining the first object image of a first object; andobtaining the second object image of a second object different from thefirst object.

The obtaining of the first object image and the second object image mayinclude obtaining the first object image; and obtaining the secondobject image by changing values of pixels of the first object image.

The obtaining of the first object image and the second object image mayinclude obtaining the first object image in which an object is locatedwithin a predefined depth of field; and obtaining the second objectimage in which the object is located outside the predefined depth offield.

The displaying of the first holographic image and the second holographicimage may include displaying, on the first depth layer, the firstholographic image having the first predefined amplitude data; anddisplaying, on the second depth layer, the second holographic imagehaving the second predefined amplitude data.

A non-transitory computer-readable recording medium may have recordedthereon a program for executing the method of an above-noted aspect ofthe disclosure on a computer.

In accordance with an aspect of the disclosure, a system for processinga computer-generated hologram (CGH) includes a CGH generation apparatusconfigured to generate a CGH; and a display apparatus configured todisplay the CGH, wherein the CGH generation apparatus is furtherconfigured to obtain a first object image corresponding to a first depthlayer and a second object image corresponding to a second depth layer,determine first predefined amplitude data based on the first objectimage and second predefined amplitude data based on the second objectimage, generate first object data including the first predefinedamplitude data and randomized first phase data, and perform apropagation using the first object data as an input, wherein thepropagation includes propagating the first object data to the seconddepth layer to obtain second object data including second amplitude dataand second phase data; replacing the second amplitude data with thesecond predefined amplitude data to obtain changed second object data;back-propagating the changed second object data to the first depth layerto obtain changed first object data including changed first amplitudedata and changed first phase data; and replacing the changed firstamplitude data included in the changed first object data with the firstpredefined amplitude data to obtain final first object data, and whereinthe CGH generation apparatus is further configured to generate the CGHbased on the final first object data, and display a first holographicimage including the first predefined amplitude data and a secondholographic image including the second predefined amplitude data byusing the CGH.

The CGH generation apparatus may be further configured to perform thepropagation a predefined number of times using the final first objectdata of a preceding iteration of the propagation as the input before thegenerating of the CGH.

The propagation may further include determining a difference between thechanged first amplitude data and the first predefined amplitude data;and repeating the propagation using the final first object data of apreceding iteration of the propagation as the input based on thedetermined difference being greater than or equal to a predefinedthreshold value.

The propagation may further include determining a difference between thechanged second amplitude data and the second predefined amplitude data;and repeating the propagation using the final first object data of apreceding iteration of the propagation as the input based on thedetermined difference being greater than or equal to a predefinedthreshold value.

The propagating of the first object data may include performing a fastFourier transform (FFT) on the first object data, and theback-propagating of the changed second object data may includeperforming an inverse FFT on the changed second object data.

The CGH generation apparatus may be further configured to obtain thefirst object image of a first object, and obtain the second object imageof a second object different from the first object.

The CGH generation apparatus may be further configured to obtain thefirst object image, and obtain the second object image by changingvalues of pixels of the first object image.

The CGH generation apparatus may be further configured to obtain thefirst object image in which an object is located within a predefineddepth of field, and obtain the second object image in which the objectis located outside the predefined depth of field.

The display apparatus may be further configured to display, on the firstdepth layer, the first holographic image including the first predefinedamplitude data, and display, on the second depth layer, the secondholographic image including the second predefined amplitude data.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the disclosure will be more apparent from the followingdescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a diagram for explaining the principle of computer-generatedholography according to an embodiment;

FIGS. 2A and 2B are diagrams for explaining 2D images for each depthlayer of an object, when generating a computer-generated hologram (CGH)of the object by using a depth map method, according to an embodiment;

FIGS. 3A and 3B are diagrams for explaining depths of field of aLambertian surface and a CGH according to an embodiment;

FIGS. 4A and 4B are diagrams for explaining a holographic imagegenerated using a random phase according to an embodiment;

FIG. 5 is a block diagram illustrating a system for processing a CGHaccording to an embodiment;

FIG. 6A is a diagram for explaining a method of obtaining a firstpredefined amplitude data and a second predefined amplitude data,according to an embodiment;

FIGS. 6B and 6C are diagrams for explaining a method of obtaining afirst predefined amplitude data and a second predefined amplitude dataaccording to an embodiment;

FIG. 7 is a diagram for explaining propagation of object data accordingto an embodiment;

FIGS. 8A-8E are diagrams for explaining a method of obtaining a phase ofobject data according to an embodiment;

FIGS. 9A and 9B are diagrams of holographic images generated accordingto the method of FIG. 8A;

FIG. 10 is a diagram for explaining propagation of object data accordingto an embodiment;

FIG. 11 is a diagram for explaining propagation of object data accordingto an embodiment;

FIG. 12 is a diagram for explaining a method of obtaining a phase ofobject data according to an embodiment;

FIG. 13 is a flow chart of a method of generating a CGH using objectdata according to an embodiment;

FIG. 14 is a flow chart of a method of generating a CGH using objectdata according to an embodiment;

FIG. 15 is a flow chart of a method of generating a CGH using objectdata according to an embodiment; and

FIG. 16 is a flow chart of a method of processing a CGH, according to anembodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings, wherein like referencenumerals refer to like elements throughout. In this regard, embodimentsmay have different forms and should not be construed as being limited tothe descriptions set forth herein. Accordingly, embodiments are merelydescribed below, by referring to the figures, to explain aspects. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items. Expressions such as “at leastone of,” when preceding a list of elements, modify the entire list ofelements and do not modify the individual elements of the list.

With respect to the terms used in embodiments, general terms currentlyand widely used are selected, however, the terms may vary according toan intention of a technician practicing in the art, an advent of newtechnology, etc. In specific cases, terms may be chosen arbitrarily, andin this case, definitions thereof will be described in the descriptionof the corresponding disclosure. Accordingly, the terms used in thedescription should not necessarily be construed as simple names of theterms, but should be defined based on meanings of the terms and overallcontents of the disclosure.

The terms, “include(s)” or “comprise(s)” should not be interpreted orunderstood as including, without exception, all of the plurality ofelements or the plurality of operations disclosed in the description,and it should be understood that some of the elements or some of theoperations may not be included, or that additional components oroperations may be further included.

Hereinafter, embodiments will be described in detail with reference tothe accompanying drawings. However, the disclosure may be implemented invarious manners, and is not limited to one or more embodiments describedherein.

FIG. 1 is a diagram for explaining a principle of computer-generatedholography according to an embodiment.

An observer may recognize an object in a space through the observer'seye ball. The observer may see the object in the space as lightreflected from the object is refracted through an eye lens on the frontof the eye ball and condensed on a retina on the back side of the eyeball. Using this principle, the principle of computer-generatedholography may be implemented.

When the focus of the observers eye lens plane W(u,v) 14 corresponds toa depth layer L1, LM or LN, it may be assumed that an image on the depthlayer L1, LM or LN has an imaging focus on a retina plane Q(x2, y2) 13.Then, a complex light wave field in a spatial light modulator (SLM)plane (or referred to as ‘CGH plane’) P(x1, y1) 15 may be calculated byback-propagating the image, formed on the retina plane 13, to the SLMplane (or CGH plane) 15, and thus, a CGH interference pattern forexpressing a CGH at the CGH plane may be obtained.

Computer-generated holography may be classified into a point cloudmethod, a polygon method, a depth map (or layer-based) method, and soforth. In the point cloud method, a surface of an object is expressedwith a number of points and an interference pattern at each point iscalculated, and thus, a precise depth may be expressed, whereas theamount of computation greatly increases according to the number ofpoints. In the polygon method, a surface of an object is expressed aspolygon meshes and an interference pattern at each polygon mesh iscalculated, and thus, the amount of computation is small even though theprecision of the object is reduced. The depth map method is alayer-based method and a method of generating a CGH using a 2D intensityimage and depth data, and the amount of computation may be determinedaccording to the resolution of an image.

Since in depth map method, a CGH is generated after modeling byapproximating an object into multi-depth using depth layers, theefficiency of calculation may be higher than that of other methods.Also, a CGH may be generated by using only 2D intensity information anddepth information such as a general picture.

In the generation of a CGH by using the depth map method, most of thecomputer-generated holography processing is occupied by Fouriertransform operations. It is obvious to those of skill in the art thatFourier transform in the processing is an operation for obtaining adistribution of diffracted images obtained by Fresnel diffraction of animage and corresponds to generalized Fresnel transform (GFT) or Fresneltransform. In embodiments, the Fourier transform may include a fastFourier transform (FFT), a GFT, a Fresnel transform, and so forth, whichare operations using the Fourier transform.

FIGS. 2A and 2B are diagrams for explaining 2D images for each depthlayer for an object, when generating a CGH of the object by using adepth map method, according to an embodiment.

Referring to FIG. 2A, an object 200 is located in a space between an eyelens plane W(u,v) 14 and an SLM plane (or CGH plane) P(x1, y1) 15.According to the depth map scheme, this space may be set to be dividedinto a predefined number of depth layers. Here, the number of depthlayers may be any number that may be changed by a user setting, forexample, the number of depth layers may be 256 or another number.

Referring to FIG. 2B, the object 200 may be modeled as depth images 220corresponding to a predefined number of depth layers. Each of the depthimages includes object data 221 to 224 of the object 200 at acorresponding depth with respect to the eye lens plane W(u,v) 14. In anembodiment, the object data 221 to 224 include information about anamplitude and phase of light for representing the object 200 at thecorresponding depth.

FIGS. 3A and 3B are diagrams for explaining depths of field of aLambertian surface and a CGH according to an embodiment.

A depth of field (DoF) is a region where a focus is sharply captured.The depth of field is a region around an object that appears sharperwhen the focus of an eye lens plane 38 corresponds to the object.

In order to compare a depth of field fora Lambertian surface and a depthof field for a CGH, distances d1, d2, and d3 by which objects (orpixels) 31 to 33 corresponding to Lambertian surfaces are spaced apartfrom the eye lens plane 38 are set to be equal to distances d1, d2, andd3 by which objects (or pixels) 34-36 of CGHs are spaced apart from theeye lens plane 38.

Referring to FIG. 3A, the objects 31-33 having the Lambertian surfacesmay emit or reflect light in all directions. That is, the objects 31 to33 having the Lambertian surfaces may emit light at a sufficient angle θto be incident upon and pass through the entire eye lens. When the focusof the eye lens plane 38 corresponds to the object 32, an imaging focusof each light emitted from the other objects 31 and 33 is formed in aregion outside a retina plane 39. Accordingly, the object 32 appearssharper and the other objects 31 and 33 appear blurred, such that theobserver may clearly recognize depths of the objects 31-33.

Referring to FIG. 3B, the objects 34-36 of the CGH emit light in limiteddirections. That is, the objects 34-36 of the CGH may emit light at alimited angle φ to be incident upon and pass through only a portion ofthe eye lens.

When the focus of the eye lens plane 38 corresponds to the object 35, animaging focus of each light emitted from the other objects 34 and 36 isformed in or near the retina plane 39. Accordingly, the objects 34 and36 appear sharp, even though they are spaced from the eye lens plane 38by the same distances as those between the objects 31 and 33 and the eyelens plane 38, respectively. Thus, the observer may not clearlyrecognize depths of the objects 34-36.

As described above, since the depth of field for a CGH may be lower thanthat for a Lambertian surface, the observer may not recognize a depth ofa holographic image.

FIGS. 4A and 4B are diagrams for explaining a holographic imagegenerated using a random phase according to an embodiment.

Referring to FIG. 4A, in order to increase the depth of field for theCGH, light emitted from an object (or a pixel) 41 may be randomlyscattered based on a randomized phase. In other words, the direction oflight emitted at the pixel 41 may be randomized according to the randomphase. Since some of the randomly scattered light may not pass throughan eye lens 42 and may not be formed in a retina 43, black spots mayappear in a holographic image as shown in FIG. 4B. In addition, sincethe light may be randomly scattered, when the focus of the eye lens 42does not correspond to the object 41, the extent to which the object 41appears blurred may be irregular.

FIG. 5 is a block diagram illustrating a system for processing a CGHaccording to an embodiment.

Referring to FIG. 5, a system 10 for processing a CGH may include a CGHgeneration apparatus 100 and a display apparatus 150. The CGH generationapparatus 100 may include a processor 112 and a memory 114. In the CGHgeneration apparatus 100 shown in FIG. 5, only components related toembodiments are shown. Therefore, it is obvious to those of skill in theart that the CGH generation apparatus 100 may further include othergeneral-purpose components in addition to the components shown in FIG.5.

The processor 112 may correspond to a processor provided in varioustypes of computing devices such as a personal computer (PC), a serverdevice, a television (TV), a mobile device (a smartphone, a tabletdevice, etc.), an embedded device, an autonomous vehicle, a wearabledevice, an augmented reality (AR) device, and an Internet of things(loT) device. For example, the processor 112 may correspond to aprocessor such as a central processing unit (CPU), a graphics processingunit (GPU), an application processor (AP), or a neural processing unit(NPU), but is not limited thereto.

The processor 112 performs overall functions for controlling the CGHgeneration apparatus 100. The processor 112 may control the CGHgeneration apparatus 100 by executing programs stored in the memory 114.For example, in the case where the CGH generation apparatus 100 isprovided in the display apparatus 150, the processor 112 may control thedisplay of a holographic image by the display apparatus 150 bycontrolling image processing by the CGH generation apparatus 100.

The display apparatus 150 may correspond to a device capable ofdisplaying a holographic image in a 3D space based on a CGH generated bythe CGH generation apparatus 100. The display apparatus 150 may includea hardware module for reproducing a hologram, such as a spatial lightmodulator (SLM) 155, and may include various types of display panelssuch as an LCD and an OLED. That is, the display apparatus 150 mayinclude various hardware modules and hardware configurations fordisplaying a holographic image, in addition to the CGH generationapparatus 100. The CGH generation apparatus 100 may be a separateindependent apparatus implemented outside the display apparatus 150. Inthis case, the display apparatus 150 may receive CGH data generated bythe CGH generation apparatus 100 implemented outside the displayapparatus 150, and may display a holographic image based on the receivedCGH data. However, the implementation manner of the CGH generationapparatus 100 and the display apparatus 150 is not limited by any oneembodiment.

The memory 114 is hardware that stores various pieces of data processedin the processor 112, and for example, the memory 114 may store CGH dataprocessed by the processor 112 and CGH data to be processed. Inaddition, the memory 114 may store various applications to be executedby the processor 112, such as hologram reproducing applications, webbrowsing applications, game applications, video applications, and soforth.

The memory 114 may include at least one of volatile memory andnonvolatile memory. The nonvolatile memory includes read only memory(ROM), programmable ROM (PROM), electrically programmable ROM (EPROM),electrically erasable and programmable ROM (EEPROM), flash memory,phase-change RAM (PRAM), magnetic RAM (MRAM), resistive RAM (RRAM),ferroelectric RAM (FRAM) and so forth. The volatile memory includesdynamic RAM (DRAM), static RAM (SRAM), synchronous DRAM (SDRAM),phase-change RAM (PRAM), magnetic RAM (MRAM), resistive RAM (RRAM),ferroelectric RAM (FRAM), and so forth. In an embodiment, the memory 114may include at least one of a hard disk drive (HDD), a solid state drive(SSD), a compact flash (CF), a secure digital (SD), a micro-securedigital (Micro-SD), a mini-secure digital (mini-SD), an extreme digital(xD), or a memory stick.

The processor 112 may determine a phase value of object data in any onedepth layer such that an amplitude value of object data in another depthlayer may satisfy a target amplitude value.

The processor 112 may obtain target amplitude values of object data in aplurality of depth layers from a plurality of 2D images that arepre-generated. For example, first and second target amplitude values ofthe object data in first and second depth layers may be obtained fromfirst and second 2D images, respectively.

The processor 112 may then set an initial amplitude value of the objectdata in the first depth layer to the first target amplitude value, andmay set an initial phase value of the object data in the first depthlayer to an arbitrary phase value.

The processor 112 may obtain an amplitude value and a phase value of theobject data in the second depth layer by propagating the object datafrom the first depth layer to the second depth layer. The processor 112may change the amplitude value of the object data in the second depthlayer to the second target amplitude value.

The processor 112 may then obtain an amplitude value and a phase valueof the object data in the first depth layer by back-propagating theobject data from the second depth layer to the first depth layer. Theprocessor 112 may change the amplitude value of the object data in thefirst depth layer to the first target amplitude value.

The processor 112 may then obtain a final phase value of the object databy repeatedly performing the processes of propagating andback-propagating the object data between the first depth layer and thesecond depth layer. In addition, the processor 112 may obtain the finalamplitude value of the object data from the first target amplitudevalue.

The processor 112 may set the amplitude value and the phase value of theobject data in the first depth layer to a final amplitude value and thefinal phase value, respectively. The processor 112 may generate a CGH byusing the object data in the first depth layer.

The processor 112 may be configured to generate a first object imagecorresponding to the first depth layer, and a second object imagecorresponding to the second depth layer.

The processor 112 may be configured to determine first predefinedamplitude data based on the first object image, and second predefinedamplitude data based on the second object image.

The processor 112 may be configured to generate first object dataincluding the first predefined amplitude data and randomized first phasedata.

The processor 112 may be configured to perform a propagation process byusing the first object data as input data. The propagation process mayinclude propagating the first object data to the second depth layer toobtain second object data including second amplitude data and secondphase data, changing the second amplitude data to the second predefinedamplitude data to obtain changed second object data, back-propagatingthe changed second object data to the first depth layer to obtainchanged first object data including changed first amplitude data andchanged first phase data, and changing, to the first predefinedamplitude data, the changed first amplitude data included in the changedfirst object data to obtain final first object data. The processor 112may be configured to generate a CGH based on the final first objectdata.

The display apparatus 150 may be configured to display a holographicimage having the first predefined amplitude data and the secondpredefined amplitude data (i.e., a first holographic image and a secondholographic image), by using the generated CGH.

FIG. 6A is a diagram for explaining a method of obtaining a firstpredefined amplitude data and a second predefined amplitude data basedon first and second 2D images 61 and 62, according to an embodiment.

A first object image 61 is a 2D image corresponding to the first depthlayer. First predefined amplitude data |A(x,y)| may be obtained based onthe first object image 61.

A second object image 62 is a 2D image corresponding to the second depthlayer. Second predefined amplitude data |B(x,y)| may be obtained basedon the second object image 62.

The first object image 61 and the second object image 62 may be 2Dimages obtained from a single object. Alternatively, the first objectimage 61 and the second object image 62 may be 2D images obtained fromdifferent objects.

In an embodiment, the first object image 61 may be an image in which anobject 63 is located within a predefined depth of field, and the secondobject image 62 may be an image in which an object 64 is located outsidethe predefined depth of field. Alternatively, the first object image 61and the second object image 62 may be images in which both of theobjects 63 and 64 are located within or outside the depth of field. Thedepth of field may be arbitrarily set. The object 63 and the object 64may be the same as or different from each other.

In embodiments, the first object image 61 may be an image in which theobject 63 is focused, and the second object image 62 may be an image inwhich the object 64 is not focused. Alternatively, the first objectimage 61 and the second object image 62 may be images in which both ofthe objects 63 and 64 are focused or not focused. The object 63 and theobject 64 may be the same as or different from each other.

In an embodiment, the first object image 61 may be an image to bedisplayed from the first depth layer, and the second object image 62 maybe an image to be displayed from the second depth layer.

The second object image 62 may be generated from the first object image61. The second object image 62 may be generated by changing values ofpixels in the first object image 61. For example, the second objectimage 62 may be generated by blurring the first object image 61 or byrendering the first object image 61.

The first and second object images 61 and 62 may include color data,such as RGB and YUV, and amplitude values of light may be obtained fromthe color data.

The processor 112 (shown in FIG. 5) may obtain the first predefinedamplitude data |A(x,y)| by obtaining the amplitude values of the lightfrom the first object image 61. In addition, the processor 112 mayobtain the second predefined amplitude data |B(x,y)| by obtainingamplitude values of light from the second object image 62.

FIGS. 6B and 6C are diagrams for explaining a method of obtaining afirst predefined amplitude data and a second predefined amplitude dataaccording to an embodiment.

A first object image 65 and a second object image 66 shown in FIGS. 6Band 6C, respectively, may be images in which different objects arecaptured. In FIGS. 6B, a string “GHIJKLABCDEF” corresponding to a firstobject is shown and in FIG. 6C, a string “STUVWMNOPQ” corresponding to asecond object is shown.

The first and second object images 65 and 66 may not be physicallyrelated to each other. For example, the first object image 65 and thesecond object image 66 may be images in which different objects areindependently captured.

Referring to FIGS. 6B and 6C, the first object image 65 is a 2D imagefor obtaining first predefined amplitude data |A(x,y)| for the firstobject in the first depth layer. The second object image 66 is a 2Dimage for obtaining second predefined amplitude data |B(x,y)| for thesecond object in the second depth layer.

In an embodiment, the first object image 65 and the second object image66 may be images in which the objects are expressed where focal lengthsof the eye lens are equal to or different from each other.

In an embodiment, the first object image 65 may be an image in which thefirst object is located within a depth of field for the first depthlayer, and the second object image 66 may be an image in which thesecond object is located within a depth of field for the second depthlayer. Alternatively, the first object image 65 may be an image in whichthe first object is located within the depth of field for the firstdepth layer, and the second object image 66 may be an image in which thesecond object is located outside the depth of field for the second depthlayer. Alternatively, the first object image 65 may be an image in whichthe first object is located outside the depth of field for the firstdepth layer, and the second object image 66 may be an image in which thesecond object is located outside the depth of field for the second depthlayer. The depth of field may be arbitrarily set.

In an embodiment, the first object image 65 and the second object image66 may be images in which the first and second objects are focused.Alternatively, the first object image 65 may be an image in which thefirst object is focused, and the second object image 66 may be an imagein which the second object 66 is not focused. Alternatively, the firstobject image 65 and the second object image 66 may be images in whichboth the first and second objects are not focused.

In an embodiment, the first object image 65 may be an image to be outputfrom the first depth layer, and the second object image 66 may be animage to be output from the second depth layer.

The processor 112 (shown in FIG. 5) may obtain the first predefinedamplitude data |A(x,y)| by obtaining amplitude values of light from thefirst object image 65. In addition, the processor 112 may obtain thesecond predefined amplitude data |B(x,y)| by obtaining amplitude valuesof light from the second object image 66.

FIG. 7 is a diagram for explaining propagating of object data accordingto an embodiment.

The object data includes information about an amplitude and a phase oflight. Amplitude data of the object data includes information about anintensity of light. An image in a depth layer may be generated based onthe amplitude data of the object data in the depth layer. In otherwords, phase data of the object data are not necessary to generate animage in a depth layer. Phase data of the object data includesinformation about propagation (for example, propagation direction) oflight. An image in another depth layer may be generated based on theamplitude data and the phase data of the object data in any one depthlayer.

Amplitude data and phase data of the object data in other layers may beobtained by propagating or back-propagating the object data from any onelayer.

By propagating first object data 71 from a first depth layer L_(l) to asecond depth layer L_(m), amplitude data and phase data of second objectdata 72 may be obtained. By back-propagating second object data 72 fromthe second depth layer L_(m) to the first depth layer L_(l), amplitudedata and phase data of the first object data 71 may be obtained.

FIGS. 8A-8E are diagrams for explaining a method of obtaining a phase ofobject data according to an embodiment.

The processor 112 (shown in FIG. 5) may set initial amplitude data offirst object data 801 to the first predefined amplitude data |A(x,y)|.The processor 112 may set initial phase data of the first object data801 to randomized phase data p_(n=1)(x, y).

The processor 112 may obtain amplitude data |B′(x,y)| and phase dataq_(n=1)(x,y) of second object data 802 by propagating the first objectdata 801 from the first depth layer to the second depth layer. Theprocessor 112 may propagate the first object data 801 from the firstdepth layer to the second depth layer to obtain the second object data802 by performing a Fourier transform (for example, a fast Fouriertransform FFT) on the first object data 801 based on a distance dbetween the first depth layer and the second depth layer.

The processor 112 may change the amplitude data |B′(x,y)| of the secondobject data 802 to the second predefined amplitude data |B(x,y)|.

FIG. 8C shows an example of a holographic image generated from thesecond object data 802 having the amplitude data |B′(x,y)|, and FIG. 8Dshows an example of a holographic image generated from changed secondobject data 803 having the second predefined amplitude data |B(x,y)|.

The processor 112 may obtain amplitude data |A′(x,y)| and phase datap_(n=2)(x,y) of first object data 804 by back-propagating the secondobject data 803 from the second depth layer to the first depth layer.The processor 112 may back-propagate the second object data 803 from thesecond depth layer to the first depth layer to obtain the first objectdata 804 by performing an inverse Fourier transform (for example, aninverse fast Fourier transform FFT⁻¹) on the second object data 803based on the distance d between the first depth layer and the seconddepth layer.

The processor 112 may then change the amplitude data |A′(x,y)| of thefirst object data 804 to the first predefined amplitude data |A(x,y)|.

FIG. 8E shows an example of a holographic image generated from the firstobject data 804 having the amplitude data |A′(x,y)|, and FIG. 8B showsan example of a holographic image generated from the changed firstobject data 801 having the first predefined amplitude data |A(x,y)I.

The processor 112 may obtain final first object data by repeatedlyperforming the loop illustrated in FIG. 8A a predefined number of timeswhile incrementing n.

The processor 112 may determine final phase data as being phase datap_(n=N+1)(x,y) of the final first object data obtained by repeating, apredefined number of times N, the loop illustrated in FIG. 8A.

Alternatively, the processor 112 may determine the final phase data asp_(n=M+1)(x,y) obtained by repeatedly performing, M times, the loopillustrated in FIG. 8A, based on a comparison between the amplitude data|A′(x,y)| of the first object data 804 in the first depth layer and thefirst predefined amplitude data |A(x,y)|. For example, the processor 112may repeatedly perform, M times, the loop illustrated in FIG. 8A until adifference between the amplitude data |A′(x,y)| of the first object data804 and the first predefined amplitude data |A(x,y)| is less than apredefined threshold value. In this case, the number of times M dependson the difference between the amplitude value |A′(x,y)| of the objectdata 804 in the first depth layer and the first target amplitude value|A(x,y)|.

Alternatively, the processor 112 may determine the final phase data asbeing phase data p_(n=T+1)(x,y) of the first object data obtained byrepeatedly performing, T times, the loop illustrated in FIG. 8A, basedon a comparison between the amplitude data |B′(x,y)| of the secondobject data 802 and the second predefined amplitude data |B(x,y)|. Forexample, the processor 112 may repeatedly perform, T times, the loopillustrated in FIG. 8A until a difference between the amplitude data|B′(x,y)| of the second object data 802 and the second predefinedamplitude data |B(x,y)| is less than a predefined threshold value. Inthis case, the number of times T depends on the difference between theamplitude value |B′(x,y)| of the object data 802 in the second depthlayer and the second target amplitude value |B(x,y)|.

FIGS. 9A and 9B are diagrams of holographic images generated accordingto the method of FIG. 8A.

The left image of FIG. 9A is a holographic image in the first depthlayer, and the right image is a holographic image in the second depthlayer.

A CGH having the first predefined amplitude data and the secondpredefined amplitude data, respectively, may be generated by the methodof FIG. 9A. The display apparatus 150 (shown in FIG. 5) may displayholographic images having the first predefined amplitude data and thesecond predefined amplitude data, respectively, based on the CGH.Accordingly, the holographic image having the first predefined amplitudedata may be displayed on the first depth layer, and the holographicimage having the second predefined amplitude data may be displayed onthe second depth layer. That is, the first object image may be displayedby the holographic image on the first depth layer, and the second objectimage may be displayed by the holographic image on the second depthlayer.

The holographic images shown in FIG. 9A are holographic images generatedby using the first and second object images illustrated in FIGS. 6B and6C, and it may be confirmed that the holographic images are displayedwith desired intensities of light in the first depth layer and thesecond depth layer, respectively.

In FIG. 9B, the left image is a holographic image on the first depthlayer, and the right image is a holographic image on the second depthlayer.

Since the final phase data of the first object data may be determined tosatisfy the first predefined amplitude data and the second predefinedamplitude data, holographic images may be expressed with desiredintensities of light in the first depth layer and the second depthlayer, respectively. Accordingly, black dots may be prevented from beinggenerated in the image, and the extent to which the image appearsblurred may be prevented from being irregular.

FIG. 10 is a diagram for explaining propagating of object data accordingto an embodiment.

A target to be generated into a holographic image may be a plurality ofobjects. FIG. 10 shows first and second object data 1001 and 1002 andthird and fourth object data 1003 and 1004 for two objects,respectively, according to an embodiment.

The processor 112 (shown in FIG. 5) may obtain amplitude data and phasedata of the second object data 1002 by propagating the first object data1001 from the first depth layer L_(l) to the second depth layer L_(m).Similarly, the processor 112 may obtain amplitude data and phase data ofthe fourth object data 1004 by propagating the third object data 1003from the first depth layer L_(l) to the second depth layer L_(m).

Only pixels corresponding to the first object data 1001 may beconsidered in a process of propagating the first object data 1001, andonly pixels corresponding to the third object data 1003 may beconsidered in a process of propagating the third object data 1003.Accordingly, the first object data 1001 and the third object data 1003may be independently propagated.

Similarly, only pixels corresponding to the second object data 1002 maybe considered in a process of back-propagating the second object data1002, and only pixels corresponding to the fourth object data 1004 maybe considered in a process of back-propagating the fourth object data1004. Accordingly, the second object data 1002 and the fourth objectdata 1004 may be independently back-propagated.

Accordingly, the processor 112 may perform processes of propagating andback-propagating the first and second object data 1001 and 1002 and thethird and fourth object data 1003 and 1004 in parallel, and may reducecalculation times.

FIG. 11 is a diagram for explaining propagating of object data accordingto an embodiment.

The object data may be propagated or back-propagated between two or moredepth layers. FIG. 11 shows object data that is propagated orback-propagated between three depth layers.

The three depth layers L_(l), L_(m), and L_(n) may be arbitrary depthlayers. A distance d1 between the first depth layer L_(l) and the seconddepth layer L_(m) and a distance d2 between the second depth layer L_(m)and the third depth layer L_(n) may be equal to or different from eachother.

By propagating first object data 1101 from the first depth layer L_(l)to the second depth layer L_(m), amplitude data and phase data of secondobject data 1102 may be obtained. By propagating the second object data1102 from the second depth layer L_(m) to the third depth layer L_(n),amplitude data and phase data of third object data 1103 may be obtained.By back-propagating the third object data 1103 from the third depthlayer L_(n) to the first depth layer L_(l), amplitude data and phasedata of the first object data 1101 may be obtained.

FIG. 12 is a diagram for explaining a method of obtaining a phase ofobject data according to an embodiment.

The processor 112 (shown in FIG. 5) may set initial amplitude data offirst object data 1201 to the first predefined amplitude data |A(x,y)|.The processor 112 may set initial phase data of the first object data1201 to randomized phase data p_(n=1)(x, y).

The processor 112 may obtain amplitude data |B′(x,y)| and phase dataq_(n=1)(x,y) of second object data 1202 by propagating the first objectdata 1201 from the first depth layer to the second depth layer. Theprocessor 112 may propagate the first object data 1201 from the firstdepth layer to the second depth layer by performing a Fourier transformon the first object data 1201 based on a distance d1 between the firstdepth layer and the second depth layer.

The processor 112 may change the amplitude data |B′(x,y)| of the secondobject data 1202 to the second predefined amplitude data |B(x,y)| toobtain second object data 1203.

The processor 112 may obtain amplitude data |C′(x,y)| and phase datar_(n=1)(x,y) of third object data 1204 by propagating second object data1203 from the second depth layer to the third depth layer.

The processor 112 may change the amplitude data |C′(x,y)| of the thirdobject data 1204 to predefined third amplitude data |C(x,y)| to obtainthird object data 1205.

The processor 112 may obtain amplitude data |A′(x,y)| and phase datap_(n=2)(x,y) of first object data 1206 by back-propagating third objectdata 1205 from the third depth layer to the first depth layer.

The processor 112 may change the amplitude data |A′(x,y)| of the objectdata 1206 to the first predefined amplitude data |A(x,y)| to obtainchanged first object data 1201.

The processor 112 may obtain final phase data of final first object databy repeatedly performing the loop illustrated in FIG. 12 whileincrementing n. In other words, the loop of FIG. 12 may be performed ntimes wherein each iteration of the loop receives as input the changedfirst object data output by the preceding iteration.

The processor 112 may determine the final phase data as p_(n=N+1)(x,y)of the first object data obtained by repeatedly performing, a predefinednumber of times N, the loop illustrated in FIG. 12.

Alternatively, the processor 112 may determine the final phase data asp_(n=M+1)(x,y) of the first object data obtained by repeatedlyperforming, M times, the loop illustrated in FIG. 12, based on acomparison between the amplitude data |A′(x,y)| of the first object data1206 and the first predefined amplitude data |A(x,y)|. In other words,the processor 112 may determine whether to perform, or to refrain fromperforming, another iteration of the loop of FIG. 12 based on thecomparison between the amplitude data |A′(x,y)| of the first object data1206 in the first depth layer and the first predefined amplitude data|A(x,y)|.

Alternatively, the processor 112 may determine the final phase data asbeing phase data p_(n=T+1)(x,y) of the first object data obtained byrepeatedly performing, T times, the loop illustrated in FIG. 12, basedon a comparison between the amplitude data |B′(x,y)| of the secondobject data 1202 and the second predefined amplitude data |B(x,y)|. Inother words, the processor 112 may determine whether to perform, or torefrain from performing, another iteration of the loop of FIG. 12 basedon the comparison between the amplitude data |B′(x,y)| of the secondobject data 1202 in the second depth layer and the second predefinedamplitude data |B(x,y)|.

Alternatively, the processor 112 may determine the final phase data asbeing phase data p_(n=S+1)(x,y) of the first object data obtained byrepeatedly performing, S times, the loop illustrated in FIG. 12, basedon a comparison between the amplitude data |C′(x,y)| of the third objectdata 1204 and the third predefined amplitude data |C(x,y)|. In otherwords, the processor 112 may determine whether to perform, or to refrainfrom performing, another iteration of the loop of FIG. 12 based on thecomparison between the amplitude data |C′(x,y)| of the third object data1204 in the third depth layer and the third predefined amplitude data|C(x,y)|.

A structure of a loop for obtaining the final phase data is not limitedto the structure of the loop illustrated in FIG. 12. In an embodiment,the loop may be configured to propagate the first object data from thefirst depth layer to the third depth layer, then to back-propagate thethird object data from the third depth layer to the second depth layer,and then to back-propagate the second object data from the second depthlayer to the first depth layer.

FIG. 13 is a flow chart of a method of generating a CGH using objectdata according to an embodiment.

In operation 1301, the processor 112 (shown in FIG. 5) may obtain theamplitude value and the phase value of the object data in the seconddepth layer by propagating the object data from the first depth layer tothe second depth layer. The processor 112 may propagate the object databy performing a Fourier transform on the object data based on a distancebetween the first depth layer and the second depth layer.

In operation 1302, the processor 112 may change the amplitude value ofthe object data in the second depth layer to a predefined second targetamplitude value.

In operation 1303, the processor 112 may obtain the amplitude value andthe phase value of the object data in the first depth layer byback-propagating the object data having the second target amplitudevalue from the second depth layer to the first depth layer. Theprocessor 112 may back-propagate the object data by performing aninverse Fourier transform on the object data based on the distancebetween the first depth layer and the second depth layer.

In operation 1304, the processor 112 may generate changed object data bychanging the amplitude value of the object data in the first depth layerto a predefined first target amplitude value.

In operation 1305, the processor 112 may generate a CGH by using thechanged object data having the predefined first target amplitude value.The final amplitude value may be determined to be the first targetamplitude value, and the final phase value may be determined to be thephase value in the first depth layer. The processor 112 may generate theCGH using the changed object data having the final amplitude value andthe final phase value.

FIG. 14 is a flow chart of a method of generating a CGH using objectdata according to an embodiment.

In operation 1401, the processor 112 (shown in FIG. 5) may set the firsttarget amplitude value and the second target amplitude value of theobject data in each of the first depth layer and the second depth layer.The first target amplitude value and the second target amplitude valuemay be obtained from pre-generated first and second images,respectively.

In operation 1402, the processor 112 may set the initial amplitude valueand the initial phase value of the object data in the first depth layer.The initial amplitude value may be set to be the first target amplitudevalue, and the initial phase value may be set to be an arbitrary phasevalue.

In operation 1403, the processor 112 may obtain the amplitude value andthe phase value of the object data in the second depth layer bypropagating the object data from the first depth layer to the seconddepth layer.

In operation 1404, the processor 112 may change the amplitude value ofthe object data in the second depth layer to a predefined second targetamplitude value.

In operation 1405, the processor 112 may obtain the amplitude value andthe phase value of the object data in the first depth layer byback-propagating the object data having the second target amplitudevalue from the second depth layer to the first depth layer. That is, inoperation 1405, the amplitude value and the phase value of the objectdata in the first depth layer may be updated.

In operation 1406, the processor 112 may generate changed object data bychanging the amplitude value of the object data in the first depth layerto a predefined first target amplitude value.

In operation 1407, the processor 112 may determine whether to repeatedlyperform operations 1403 to 1406. The processor 112 may determine toproceed to operation 1408 based on the result of the determination atoperation 1407. For example, the determination at operation 1407 may bemade based on the number of times that operations 1403 to 1406 have beenrepeatedly performed. Alternatively, the processor 112 may determine toproceed to operation 1408 based on a comparison of the amplitude valueof the changed object data in the first depth layer of operation 1405and the first target amplitude value. Alternatively, the processor 112may determine to proceed to operation 1408 based on a comparison of theamplitude value of the object data in the second depth layer ofoperation 1403 and the second target amplitude value.

In operation 1408, the processor 112 may generate a CGH by using thechanged object data having the first target amplitude value. The finalamplitude value may be determined to be the first target amplitudevalue, and the final phase value may be determined to be the phase valuein the first depth layer finally obtained by repeating operations 1403to 1406. The processor 112 may generate the CGH using the object datahaving the final amplitude value and the final phase value.

FIG. 15 is a flow chart of a method of generating a CGH using objectdata according to an embodiment.

In operation 1501, the processor 112 (shown in FIG. 5) may obtain theamplitude value and the phase value of the object data in the seconddepth layer by propagating the object data from the first depth layer tothe second depth layer. In an embodiment, operation 1501 may besubstituted with an operation of propagating the object data from thefirst depth layer to the third depth layer.

In operation 1502, the processor 112 may change the amplitude value ofthe object data in the second depth layer to a predefined second targetamplitude value. In an embodiment, operation 1502 may be substitutedwith an operation of changing the amplitude value of the object data inthe third depth layer to a predefined third target amplitude value.

In operation 1503, the processor 112 may obtain the amplitude value andthe phase value of the object data in the third depth layer bypropagating the object data having the second target amplitude valuefrom the second depth layer to the third depth layer. In an embodiment,operation 1503 may be substituted with an operation of back-propagatingthe object data from the third depth layer to the second depth layer.

In operation 1504, the processor 112 may change the amplitude value ofthe object data in the third depth layer to the predefined third targetamplitude value. In an embodiment, operation 1504 may be substitutedwith an operation of changing the amplitude value of the object data inthe second depth layer to the predefined second target amplitude value.

In operation 1505, the processor 112 may obtain the amplitude value andthe phase value of the object data in the first depth layer byback-propagating the object data having the third target amplitude valuefrom the third depth layer to the first depth layer. In an embodiment,operation 1505 may be substituted with an operation of back-propagatingthe object data from the second depth layer to the first depth layer.

In operation 1506, the processor 112 may generate changed object data bychanging the amplitude value of the object data in the first depth layerto the predefined first target amplitude value.

In operation 1507, the processor 112 may generate a CGH by using thechanged object data having the predefined first target amplitude value.

FIG. 16 is a flow chart of a method of processing a CGH, according to anembodiment.

In operation 1601, the CGH generation apparatus 100 (shown in FIG. 5)may obtain a first object image corresponding to a first depth layer,and a second object image corresponding to a second depth layer. The CGHgeneration apparatus 100 may generate or obtain the first and secondobject images independently. Alternatively, the CGH generation apparatus100 may generate the first object image and then generate the secondobject image by modifying the first object image.

In operation 1602, the CGH generation apparatus 100 may determine firstpredefined amplitude data based on the first object image and secondpredefined amplitude data based on the second object image.

In operation 1603, the CGH generation apparatus 100 may generate firstobject data comprising the first predefined amplitude data andrandomized first phase data.

In operation 1604, the CGH generation apparatus 100 may perform apropagation process using the first object data as an input.

The propagation process may include propagating the first object data toa second depth layer to obtain second object data including secondamplitude data and second phase data. The first object data may bepropagated by performing an FFT on the first object data. In addition,the propagation process may further include changing the secondamplitude data to the second predefined amplitude data to obtain changedsecond object data.

The propagation process may further include back-propagating the changedsecond object data to the first depth layer to obtain changed firstobject data including changed first amplitude data and changed firstphase data. The changed second object data may be back-propagated byperforming an inverse FFT on the changed second object data.

The propagation process may further include changing, to the firstpredefined amplitude data, the changed first amplitude data included inthe changed first object data to obtain final first object data.

The CGH generation apparatus 100 may generate a CGH based on the finalfirst object data.

The display apparatus 150 (shown in FIG. 5) may display holographicimages having the first predefined amplitude data and the secondpredefined amplitude data, respectively, based on the CGH. The displayapparatus 150 may display the holographic image having the firstpredefined amplitude data on the first depth layer, and display theholographic image having the second predefined amplitude data on thesecond depth layer. In this case, the display apparatus 150 is regardedas an ideal device without aberrations or the like. Accordingly, thefirst object image may be displayed by the holographic image on thefirst depth layer, and the second object image may be displayed by theholographic image on the second depth layer.

Embodiments described above may be written in a program that may beexecuted on a computer and implemented on a general-purpose digitalcomputer that operates the program using a non-transitorycomputer-readable recording medium. Also, the structure of the data usedin embodiments may be recorded on a non-transitory computer-readablerecording medium via various units. Examples of the non-transitorycomputer-readable recording medium include magnetic storage media (e.g.,ROM, floppy disks, hard disks, etc.), optical recording media (e.g.,CD-ROMs, or DVDs), etc.

It should be understood that embodiments described herein should beconsidered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each embodimentshould typically be considered as available for other similar featuresor aspects in other embodiments. While one or more embodiments have beendescribed with reference to the figures, it will be understood by thoseof ordinary skill in the art that various changes in form and detailsmay be made therein without departing from the spirit and scope asdefined by the following claims and their equivalents.

What is claimed is:
 1. A method for processing a computer-generatedhologram (CGH), the method comprising: obtaining a first object imagecorresponding to a first depth layer and a second object imagecorresponding to a second depth layer; determining first predefinedamplitude data based on the first object image and second predefinedamplitude data based on the second object image; generating first objectdata comprising the first predefined amplitude data and randomized firstphase data; and performing a propagation process using the first objectdata as an input, the propagation process comprising: propagating thefirst object data to the second depth layer to obtain second object datacomprising second amplitude data and second phase data; replacing thesecond amplitude data with the second predefined amplitude data toobtain changed second object data; back-propagating the changed secondobject data to the first depth layer to obtain changed first object datacomprising changed first amplitude data and changed first phase data;and replacing the changed first amplitude data included in the changedfirst object data with the first predefined amplitude data to obtainfinal first object data, wherein the method further comprises:generating a CGH based on the final first object data; and displaying afirst holographic image comprising the first predefined amplitude dataand a second holographic image comprising the second predefinedamplitude data based on the CGH.
 2. The method of claim 1, furthercomprising: performing the propagation process a predefined number oftimes using the final first object data of a preceding iteration of thepropagation process as the input before the generating of the CGH. 3.The method of claim 1, wherein the propagation process further comprises: determining a difference between the changed first amplitudedata and the first predefined amplitude data; and repeating thepropagation process using the final first object data of a precedingiteration of the propagation process as the input based on thedetermined difference being greater than or equal to a predefinedthreshold value.
 4. The method of claim 1, wherein the propagationprocess further com prises: determining a difference between the changedsecond amplitude data and the second predefined amplitude data; andrepeating the propagation process using the final first object data of apreceding iteration of the propagation process as the input based on thedetermined difference being greater than or equal to a predefinedthreshold value.
 5. The method of claim 1, wherein the propagating ofthe first object data comprises performing a fast Fourier transform(FFT) on the first object data, and wherein the back-propagating of thechanged second object data comprises performing an inverse FFT on thechanged second object data.
 6. The method of claim 1, wherein theobtaining of the first object image and the second object imagecomprises: obtaining the first object image of a first object; andobtaining the second object image of a second object different from thefirst object.
 7. The method of claim 1, wherein the obtaining of thefirst object image and the second object image comprises: obtaining thefirst object image; and obtaining the second object image by changingvalues of pixels of the first object image.
 8. The method of claim 1,wherein the obtaining of the first object image and the second objectimage comprises: obtaining the first object image in which an object islocated within a predefined depth of field; and obtaining the secondobject image in which the object is located outside the predefined depthof field.
 9. The method of claim 1, wherein the displaying of the firstholographic image and the second holographic image comprises:displaying, on the first depth layer, the first holographic image havingthe first predefined amplitude data; and displaying, on the second depthlayer, the second holographic image having the second predefinedamplitude data.
 10. A non-transitory computer-readable recording mediumhaving recorded thereon a program for executing the method of claim 1 ona computer.
 11. A system for processing a computer-generated hologram(CGH), the system comprising: a CGH generation apparatus configured togenerate a CGH; and a display apparatus configured to display the CGH,wherein the CGH generation apparatus is further configured to: obtain afirst object image corresponding to a first depth layer and a secondobject image corresponding to a second depth layer, determine firstpredefined amplitude data based on the first object image and secondpredefined amplitude data based on the second object image, generatefirst object data comprising the first predefined amplitude data andrandomized first phase data, and perform a propagation using the firstobject data as an input, wherein the propagation comprises: propagatingthe first object data to the second depth layer to obtain second objectdata comprising second amplitude data and second phase data; replacingthe second amplitude data with the second predefined amplitude data toobtain changed second object data; back-propagating the changed secondobject data to the first depth layer to obtain changed first object datacomprising changed first amplitude data and changed first phase data;and replacing the changed first amplitude data included in the changedfirst object data with the first predefined amplitude data to obtainfinal first object data, and wherein the CGH generation apparatus isfurther configured to generate the CGH based on the final first objectdata, and display a first holographic image comprising the firstpredefined amplitude data and a second holographic image comprising thesecond predefined amplitude data by using the CGH.
 12. The system ofclaim 11, wherein the CGH generation apparatus is further configured toperform the propagation a predefined number of times using the finalfirst object data of a preceding iteration of the propagation as theinput before the generating of the CGH.
 13. The system of claim 11,wherein the propagation further comprises: determining a differencebetween the changed first amplitude data and the first predefinedamplitude data; and repeating the propagation using the final firstobject data of a preceding iteration of the propagation as the inputbased on the determined difference being greater than or equal to apredefined threshold value.
 14. The system of claim 11, wherein thepropagation further comprises: determining a difference between thechanged second amplitude data and the second predefined amplitude data;and repeating the propagation using the final first object data of apreceding iteration of the propagation as the input based on thedetermined difference being greater than or equal to a predefinedthreshold value.
 15. The system of claim 11, wherein the propagating ofthe first object data comprises performing a fast Fourier transform(FFT) on the first object data, and wherein the back-propagating of thechanged second object data comprises performing an inverse FFT on thechanged second object data.
 16. The system of claim 11, wherein the CGHgeneration apparatus is further configured to obtain the first objectimage of a first object, and obtain the second object image of a secondobject different from the first object.
 17. The system of claim 11,wherein the CGH generation apparatus is further configured to obtain thefirst object image, and obtain the second object image by changingvalues of pixels of the first object image.
 18. The system of claim 11,wherein the CGH generation apparatus is further configured to obtain thefirst object image in which an object is located within a predefineddepth of field, and obtain the second object image in which the objectis located outside the predefined depth of field.
 19. The system ofclaim 11, wherein the display apparatus is further configured todisplay, on the first depth layer, the first holographic imagecomprising the first predefined amplitude data, and display, on thesecond depth layer, the second holographic image comprising the secondpredefined amplitude data.